FIELD OF THE INVENTION
The invention relates to a method for quickly controlling the output of a power plant having a turbo-generator set with a steam turbine and a generator, wherein energy storage present during a plant process is activated in order to set an additional generator output. The invention also relates to an apparatus for carrying out the method.
Reliable power supply in an electric power supply system presupposes careful tuning between the generation of electric power by a number of power units and the tapping of that energy by a number of consumers in an electricity distribution system. If the generation and tapping of the electric power are equal, the system frequency, which is an essential parameter in an electrical system, is constant. Its nominal value is, for example, 50 Hz in the European interconnected system. A frequency deviation which occurs, for example, due to the failure of a power unit or to the connection or disconnection of a consumer, can be regarded as a measure of an increase or drop in the generator output. A further task in addition to correcting frequency deviations within a power supply system is maintaining a prescribed interchange power at coupling points to subsystems of which the distribution system (interconnected system or separate network) is composed. One requirement therefore is the availability of a quick increase in output of a power unit within seconds.
Possibilities for quickly controlling the output or power and providing frequency back-up control are described in a printed publication entitled "VGB Kraftwerkstechnik" VGB Power Plant Engineering!, No. 1, January 1980, pages 18 to 23.
Although a plurality of intervention possibilities which can be carried out simultaneously or alternatively exist for quickly changing the output within the range of seconds (seconds reserve), a change in the fuel supply is required for a permanent change in the output of a power unit. In a fossil-fuel-fired power station, control valves of the steam turbine which are held in advance in the throttled position are therefore opened within the first seconds for the purpose of bridging delay times, and available steam accumulators are thereby activated and discharged virtually without delay. In addition to an increase in output due to the cancellation of the throttling of control valves of the steam turbine, preheaters which are provided in the water-steam circuit of the steam turbine and are heated through the use of extraction steam from the steam turbine are disconnected. A condenser flow which is simultaneously passed through the low-pressure preheater can be stopped and increased again within a few seconds. That measure for quickly controlling the output in fossil-fuel-fired power units by disconnecting the preheaters with a condensate stop is also described, for example, in German Patent DE 33 04 292 C2.
It is therefore customary to make use of a control device in order to regulate and/or control the quick seconds reserve, that is to say for the purpose of a controlled loading of steam flows to regenerative preheaters and/or heating condensers, as well as of the process steam and the condensate in the water-steam circuit of the steam turbine of a power unit. The control device throttles the supply of steam to preheaters, throttles the process steam and/or throttles the condensate, for the purpose of quickly controlling the output, that is to say of activating the seconds reserve. In that case, desired setting values for control valves at turbine extraction points and for control elements for setting condensate are formed in such a way that a required additional generator output is achieved. However, a disadvantage thereof is that it is extraordinarily difficult to coordinate the required rate of change in output and the output amplitude with other process variables, in particular with temperature changes in preheating trains and/or heating condensers, as well as with discharging the auxiliary condensate. Moreover, the priorities of the use of the individual measures for quickly controlling the output are not taken into account. In addition, because of the usually nonlinear control system, control quality has not been particularly high to date.